The most affordable car insurance options in the US are Geico, USAA, Progressive, and State Farm. According to various sources, these companies offer the cheapest car insurance rates for liability-only coverage, lower coverage policies, and families with teen drivers. However, it is important to note that the cheapest car insurance may not always provide the best coverage, and it is recommended to compare quotes from several insurers to find the best value for your money. Additionally, some of these companies may have certain eligibility requirements or restrictions, such as USAA only being available to military members, veterans, and their families. It is also worth considering factors such as customer satisfaction, claims handling, and discounts when choosing a car insurance company.